This invention relates to a process for the removal of ammonia, hydrogen sulfide and hydrogen cyanide from gases containing these substances. More particularly, the present invention relates to the process for removing said substances from coke plant gases by washing the gas with metallic salts.
Processes are known in the art involving the use of an aqueous alkali solution in the form of iron sulfate as a gas absorption agent. In this process, ammonia from the gas is converted into ammonium sulfate (NH.sub.4).sub.2 SO.sub.4, the majority of the hydrogen sulfide removed from the gas is converted into iron sulfide, FeS, and the hydrogen cyanide removed from the gas is converted into iron cyanide compounds. Most of these known processes provide for the drawing off of a portion of the absorption agent and treating it with oxygen or gases containing oxygen in an oxidizer. During the course of this treatment, elementary sulfur is obtained from the iron sulfide and drawn off in the form of flowers or sulfur. This process yields iron hydroxide which is then returned for further washing of gases.
In all of these known processes, they have features that are common, namely, they require the constant addition of iron sulfate for the formation of ammonium sulfate and the formation of the iron cyanide compounds; and secondly, the ammonium sulfate and the iron compounds that have resulted from the process must be withdrawn from the circulating system. It follows, therefore, that these known processes are severely limited since even if caustic alkali can be purchased at favorable terms, it is no longer economically feasible to produce crystalline ammonium sulfate since the requirements for products containing ammonia can be supplied more economically by other processes. Moreover, the present ecological conditions necessitate a total elimination to discharging cyanide compound which is poisonous.
A more comprehensive disclosure and discussion of known processes for the treating of coke oven gases is given in Vol. 2 of "Chemistry of Coal Utilization" by National Research Council Committee published by John Wiley & Sons, 1945.